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Principles, characteristics and solutions for cracks generated by grinding workpieces by grinding wheels
When high-speed grinding takes place, the heat generated doesn’t just lead to grinding burns; it also causes a significant number of relatively regular cracks—known as grinding cracks—to appear on the workpiece surface. These cracks not only mar the appearance of the components but also have a direct impact on their quality.
Grinding cracks differ significantly from quenching cracks that typically occur during conventional heat treatment. Unlike quenching cracks, grinding cracks are confined to the grinding surface, with a shallow depth that remains fairly consistent across the affected area. Mild grinding cracks often appear as straight lines perpendicular to—or nearly parallel with—the grinding direction, arranged in a regular pattern. This constitutes the first type of crack. More severe cases result in a tortoise-shell-like appearance, forming a closed network resembling a grid. When subjected to acid etching, these cracks become distinctly visible, classifying them as the second type of crack.
To prevent grinding cracks, it's essential to focus on minimizing the grinding heat. Here are some practical strategies:
**Grinding Process Adjustments:**
In dry grinding operations, the material removal rate should be kept low to limit heat generation. Wet grinding, on the other hand, employs grinding fluids, which come in both water-based and oil-based varieties. Water-based fluids generally offer superior cooling compared to oil-based ones.
**Grinding Wheel Selection:**
Choosing the right grinding wheel can mitigate the risk of cracks. Opting for softer grinding wheels helps dissipate heat more effectively. Additionally, selecting sharper abrasive materials can reduce the heat produced during the grinding process. Distributing the grinding margin between coarse and fine stages is another effective approach. Coarse grinding uses a softer wheel with larger grit size to allow aggressive material removal while improving efficiency. Fine grinding follows with a finer wheel to achieve precision, reducing the likelihood of cracks by decreasing the amount of material removed per pass. Slowing down the grinding wheel’s feed rate is also an efficient method to reduce cracking.
All these measures collectively aim to minimize heat generation during grinding, thereby reducing the incidence of cracks during the machining process. Proper implementation of these techniques ensures higher-quality parts and reduces the risk of surface damage caused by excessive heat.